1. Field of the Invention
This invention relates to ATM switches which use buffers to cope with multiple service classes containing service categories corresponding to CBR, VBR and Best Effort Classes, for example.
This application is based on Patent Application No. Hei 10-137175 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, there are provided a variety of technologies regarding the ATM networks and ATM switches (where “ATM” is an abbreviation for “Asynchronous Transfer Mode”).
For example, the paper of Japanese Patent Application, Publication No. Hei 7-240752 discloses an example of the ATM switch which is designed to manage communication quality with respect to every service class. Herein, quality control is made by the setting of a switching path in response to QCC tags representing quality classes for services requested by cells.
The paper of Japanese Patent Application, Publication No. Hei 7-193583 discloses an example of the ATM multiplexing processing employed in the B-ISDN subscriber access system (where “B-ISDN” is an abbreviation for “Broadband Integrated Services Digital Network”), which provides an efficient and fair way for use of resources of the networks. Herein, input cell data are subjected to classification according to QOS (i.e., quality of service) classes and scheduling control while connection state management is effected between the network operator and ATM multiplexing processing device.
The paper of Publication No. Hei 9-507738 (which publishes the contents of Japanese translation of the International Patent Application No. PCT/FI95/00282, International Publication No. WO95/32570) discloses an example of the technology for prioritization of traffics in the ATM networks. Herein, cells are transmitted by means of buffers which are exclusively provided for a specific service class within different service classes of the ATM network. In order to concentrate resources on the subscriber application(s) at a time while maintaining the trunk network as simple as possible, division of the service classes is made by only the VPI (i.e., virtual path identifier) of the header of the cell.
The paper of Japanese Patent Application, Publication No. Hei 7-321796 disclose a virtual path shaping device for the ATM network, in which cells of different service qualities are accumulated in different buffers respectively, so that the cells of high-quality service are firstly output.
The paper of Japanese Patent Application, Publication No. Hei 10-13416 discloses an example of the ATM switch which provides output buffers with respect to different service categories corresponding to CBR, RtVBR, NrtVBR and Best Effort classes (where “Rt” denotes “real-time” while “Nrt” denotes “non-real-time”). Each of those buffers is given a specific degree of priority in cell transfer. Herein, only when cells do not exist in all of the high-priority buffers, the cell transfer is performed.
In addition, estimation is performed using the conventional real-time call acceptance control method, which merely copes with a single class, to estimate a cell loss ratio for the traffics multiplexing calls of multiple service categories. After the estimation, the cell loss ratio for the low-priority service category is estimated under an assumption that all of the lost cells belong to the low-priority service category.
As described above, the conventional technology is designed to execute the cell transfer only when the cells do not exist in all of the high-priority buffers within the output buffers of the ATM switch, which are provided to cope with the different service categories respectively and each of which is given a specific degree of priority in cell transfer.
FIG. 9 is a block diagram showing a configuration of the output buffers provided within the ATM switch. Herein, there are provided four types of the buffers, i.e., CBR buffers, RtVBR buffers, NrtVBR buffers and “Best Effort Classes” buffers. Using a multiplexer and the above buffers, it is possible to configure an apparatus and method for multi-service-class ATM call acceptance control.
However, the aforementioned technology suffers from problems, as follows:                (1) In the case where the user needs only a certain service category (e.g., CBR) within the service categories, it is unnecessary to provide the buffers regarding the other service categories. In this case, there occurs a reduction in a use efficiency of the buffers. Because, the ATM switch lacks a function to define the buffer(s) to be related to only the service category which is requested by the user.        (2) The conventional technology designs the ATM switch such that the buffers are fixedly used for the prescribed service categories respectively. So, the ATM switch cannot cope with addition of a new service category and deletion of the service category. Because, the ATM switch lacks a function to define the buffer(s) to cope with the addition and deletion of the service category.        